Zinc base alloy



. attests zmo BASE ALLOY Lincoln 8. Gifford, Greencastle, Ind., and Harold L. Maxwell, Wilmington, Del., assignors to The American Zinc Products Company, Greencastle, Ind., a corporation of Indiana No Drawing. Application April '23, 1938,

Serial No. 203,812

(c1.75-'-1vs) 6 Claims.

This invention relates to zinc base alloys and is more particularly directed to zinc base alloys adapted for rolling and to improved engravers plates fabricated of such alloys.

The photoengraving trade requires a 'zinc plate which is hard and stiff enough at room temperatures that it will retain its flatness under ordinary conditions of handling, but the plate must not be so hard that it cannot readily be cut. In the course of their use,photoengravers zinc plates -must be cut and routed and the plates must be .of such a character that there is no undue dulling of the routing tool. While the plates must be stiff enough to retain flatness under ordinary handling, they must nevertheless be flexible enough that they may readily be flattened if bent in etching or during the course of their use.

An engravers plate adapted for general use may satisfactorily have a Rockwell hardness of about H88 to about H94. Harder or softer plates are sometimes required for special purposes and plates particularly adapted for dry mat battering, for instance, should run a Rockwell hardness of about H98 to H102.

The Rockwell hardness scale mentioned is that customarily used for non-ferrous metals and is the Rockwell hardness scale H" described in American Society of Testing Materials Standard Methods. The hardness is determined with a A, inch diameter penetrator ball with a major load of 60 kilograms appliedin five seconds from the time of trigger release to full load and then allowed to penetrate for ten seconds.

A satisfactory engravers plate must not only have a proper hardness at room temperatures but additionally should not soften excessively during the heating incident to its use. Upon the burning in of the etching powder a zinc plate is subjected to temperatures up to about 350 F. An entirely satisfactory plate should not soften more than two to four points Rockwell during the normal heating incident to its use.

in grain andthey will not etch smoothly. Undue softening upon heating is frequently encountered .and such plates are not well adapted for use in photoengraving.

It is an object of our invention to provide an alloy suitable for rolling to make improved engravers plates. It is a further object of our invention to provide engravers platesof excellent physical character and of improved etching characteristics.

Astill further object of our invention is to provideengravers plates of predetermined hardness and which do not soften excessively upon the heating incident to their use. A still further object of our invention is to provide engravers plates which are amenable to smooth and uniform etching and with which clean, sharp lines with bright, metallic-appearing bottoms are obtained. Further objects of our invention will appear hereinafter.

These and other objects of our invention are attained by the provision of an aluminum-magnesium-zinc alloy which can readily be rolled to produce engraversplates of excellent character. The zinc base alloy includes from about 0.05 per cent to 0.4 per cent of aluminum, from about- 0.0004 per cent to 0.009 per cent of magnesium,

the balance being zinc 99.85 per cent or preferably 99.99+ per cent pure zinc metal.

The use of aluminum in the aluminum-magnesium-zinc alloys of our invention efiectuate, particularly in combination with magnesium, a most satisfactory improvement in the character of engravers plates. The use of from about 0.05 per cent to 0.4 per-cent of aluminum causes the zinc base alloys of our invention to be etched smoothly and uniformly. The lines etched are cleaner by reason of the presence of aluminum in the alloy and are without pimples or irregularities. The bottoms are bright, metallic appearing and the etching of the plate is characterized by a line grain.

The aluminum should be used in an amount between about 0.05 per cent and 0.4 per cent by weight of the total alloy to obtain the results of our invention. The use of a substantially smaller quantity of aluminum does not lead to a realization of the advantages of our invention in the fullest measure and the use of a substantially largeramount of aluminum is disadvantageous because it reduces etching speed.

The zinc base engravers plates of our invention include from about 0.0004 per cent to 0.009 per cent by weight of magnesium. The magnesium in combination with aluminum leads to the produc- 2 A tion of engravers plates of excellent character and by adjusting the magnesium content of the plates within. the range indicated the hardness of the plates can be controlled and varied from a Rockwell hardness of about H70 to H108 without disadvantageously changing their etching speed or etching characteristics.

The amount of magnesium to use in any specific instance depends upon theamount of other metals in the alloy and upon the specific use for which the engravers plates are intended. 1 With a zinc base alloy containing about 0.2 per cent of aluminum, the use of 0.0007 per cent of magnesium leads to the production of engravers plates having a Rockwell hardness of from about H90 to H94. Upon increasing the magnesium content to about 0.0025 per cent the hardness of the zinc base alloyincreased .to about H98 to H100. Upon further increaseof magnesium content the hardness of the plates obtained rose to H100 to H108.

The hardness of the zinc base alloy plates containing aluminum and magnesium according to I our invention was substantially unaffected by the temperatures commonly used in burning in etching powder and the variation in hardness amounted to only about two to four points on the Rockwell hardness scale.

The aluminum may advantageously be added to the zinc base by first making an alloy containing for instanceone part by weight of aluminum and two parts by weight of zinc in a suitable small furnace by heating the zinc to approximately 1000" F. and then adding the aluminum in either sheet or pig form which will dissolve readily in zinc at this temperature. An alloy of of the zinc metal. The cadmium content of the zinc should also be as low as is economically feasible and in general no more than about 0.01 per cent of cadmium should be present. In genera], it is our preferred practice toemploy a zinc base metal containing 99.85 per cent or more zinc while-more'specifically it will be found advantageous to use the high-grade zinc known as 9999+ per cent pure.

A zinc base alloy typical of our invention and which has been found quite successful for general use contained about 0.2 per cent of aluminum, 0.000! per centof magnesium, and the ,balance zinc metal which contained 0.002 per cent lead and 0.002 per cent cadmium The sine metal of this example is of the type designated inthetrade as 9999+ per centpure.

It will be understood that while we have shown certain illustrative alloy compositions, one skilled in the art without departing from the spirit of our invention may readily produce numerous aluminum-magnesium-zinc alloys well adapted Y for use in the fabrication of engravers plates.

We claim: 1. A zinc base alloy containing from about 0.05

per cent to 0.4 per cent of aluminum, about 0.000!

per cent to 0.009 per cent of magnesium and the .balance high grade zinc. 2. A zinc base alloy containing from about 0.05

per cent to 0.4 per cent of aluminum, about 0.000!

per cent to 0.009 per cent magnesium, and the balance zinc metal containing 99.99 per cent of-,

more zinc.

3. A rolled engravers plate made of a zinc base alloy containing about 0.05 per cent to 0.4 per cent of aluminum, about 0.0004 per cent to 0.009 vper cent magnesium and the balance zinc metal containing 99.99 per cent or more zinc.

4. A rolled engravers plate made of a zinc basealloy containing about 0.2 per cent of aluminum,- about 0.0007 per cent of magnesium and the bal ance zinc metal containing 99.99 per cent or more zinc.

5. A rolled engravers plate made of a zinc base alloy containing about 0.2 per cent aluminum,

about 0.0025 per cent magnesium and the balance zinc metal containing 99.99 per cent or. more nine.

6. A zinc alloy composed of .10% to .4% of aluminum, .001% to .009% of magnesium, the

balance being nine of high purity containing at least 99.99% zinc.

. LINCOLN S. GIFPORD.

HAROLD L. MAXWELL. 

